The hematopoietic system is a life-long cell renewal process whereby a defined stem cell population gives rise to a larger population of mature, differentiated blood cells (Dexter T M. Stem cells in normal growth and disease. Br Med J 1987; 195:1192-1194) of at least nine different cell lineages (erythrocytes, platelets, eosinophils, basophils, neutrophils, monocytes/macrophages, osteoclasts, and lymphocytes) (Metcalf D. The Molecular Control of Blood Cells. 1988; Harvard University Press, Cambridge, Mass.). Stem cells are also ultimately responsible for regenerating bone marrow following treatment with cytotoxic agents or following bone marrow transplantation.
The major dose-limiting toxicities of most standard anti-neoplastic drugs are related to bone marrow suppression, which if severe and prolonged, can give rise to life-threatening infectious and hemorrhagic complications. Myelosuppression is predictable and has been reported to be dose-limiting in greater than 50% of single-agent Phase I trials cytotoxic compounds (Merrouche Y, Catimel G, Clavel M. Hematopoietic growth factors and chemoprotectants; should we move toward a two-step process for phase I clinical trials in oncology? Ann Oncol 1993; 4:471-474). The risk of infection is directly related to the degree of myelosuppression as measured by the severity and duration of neutropenia (Brody G P, Buckley M, Sathe Y S, Freireich E J. Quantitative relationship between circulating leukocytes and infections with acute leukemia. Ann In Med 1965; 64:328-334).
The control of hematopoiesis involves the interplay of a variety of cytokines and growth factors during various stages of the hematopoietic cascade, including early pluripotent stem cells and mature circulating effector cells. These regulatory molecules include granulocyte colony stimulating factor (G-CSF), granulocyte-macrophage stimulating factor (GM-CSF), macrophage-colony stimulating factor (M-CSF), and a variety of interleukins which have overlapping, additive and synergistic actions which play major roles in host defense. Mechanistically, this is accomplished by enhancing the production of granulocytes and macrophages, as well as by the activation of effector cell functions (Moore M A S. Hemopoietic growth factor interactions: in vitro and in vivo preclinical evaluation. Cancer Surveys 1990; 9:7-80). These coordinated activities support optimal host defences which are necessary for fighting bacterial, viral and fungal infections.
Strategies to prevent or reduce the severity of neutropenia and myelotoxicity include the use of hematopoietic growth factors and/or other hematopoietic cytokines. Such treatments are becoming common practice, in that they offer the potential of increased doses of cytotoxic agents that may improve the therapeutic efficacy of antineoplastic agents, and reduce the morbidity associated with their use (Steward W P. Granulocyte and granulocyte-macrophage colony stimulating factors, Lancet 1993; 342:153-157). Clinical studies have demonstrated the G-, GM- and/or M-CSF may reduce the duration of neutropenia, accelerate myeloid recovery, and reduce neutropenia-associated infections and other infectious complications in patients with malignancies who are receiving cytotoxic chemotherapy or in high infectious-risk patients following bone marrow transplantation (Steward WP. Granulocyte and granulocyte-macrophage colony stimulating factors, Lancet 1993; 342:153-157 and Munn D H, Cheung N K V. Preclinical and clinical studies of macrophage colony-stimulating factor. Semin Oncol 1992; 19:395-407).
Synthetic peptides have been reported to induce the synthesis and release of hematopoietic mediators, including m-CSF from bone marrow stromal elements (see U.S. patent application Ser. No. 08/001,905).
We have now found certain novel non-peptide compounds which have a stimulative effect on myelopoietic cells. They are useful in stimulating myelopoiesis in patients suffering from reduced myelopoietic activity, including bone marrow damage, agranulocytosis and aplastic anemia including patients having depressed bone marrow function due to immunosuppressive treatment to suppress tissue reactions i.e. in bone marrow transplant surgery. They may also be used to promote more rapid regeneration of bone marrow after cytostatic chemotherapy and radiation therapy for neoplastic and viral diseases. They may be of particular value where patients have serious infections due to a lack of immune response following bone marrow failure. They are also useful in the treatment and prevention of viral, fungal and bacterial disease.